Strong coupling effects in noncommutative spaces from OM theory and supergravity

We show that a four-parameter class of (3 + 1)-dimensional NCOS theories ca n be obtained by dimensional reduction on a general 2-torus from OM theory. Compactifying tale spatial directions of NCOS theory on a 2-torus, we stud y the transformation properties under the SO(2, 2; Z) T-duality group. We t hen discuss non-perturbative configurations of non-commutative super Yang-M ills theory. In particular, we calculate the tension for magnetic monopoles and (p, q) dyons and exhibit their six-dimensional origin, and construct a supergravity solution representing an instanton in the gauge theory. We al so compute the potential for a monopole-antimonopole in the supergravity ap proximation. (C) 2001 Elsevier Science B.V. All rights reserved.